(Fabricius, 1780)
Description (shell):
Broadly oval, about one and a half times long as wide. Not highly arched, keel scarcely developed but beaks pronounced. Sculpture of distinct growth lines and some very fine granulation. Head valve with eight major notches on anterior ventral edge; intermediate valves with one major notch on each side, articulamentum comprising a single process with smooth, evenly concave margin. Girdle rather broad, thin, appearing leathery, reddish brown, with minute, sparsely distributed granules, fringed with tiny, somewhat flattened marginal spines (T. marmoreus-detail).
Size:
Up to 40 mm long.
Colour:
Shell valves smooth and glossy, chestnut-brown with variable white or fawn marbling.
Habitat:
Lower shore and sublittoral.
Distribution:
Predominantly northern distribution (Distr. T. marmoreus).